<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>position-absolute</title>
    <style type="text/css">
        div div{
            border: 1px solid #f00;
            height: 100px;
            width: 160px;
            float: left;
        }
        #box-absolute{
            position: absolute;
            top: 30px;
            left: 30px;
            background-color: #b4b4b4;
        }
    </style>
</head>
<body>
<div>
    <div>块1</div>
    <div id="box-absolute">块2</div>
    <div>块3</div>
</div>
</body>
</html>